Computer networks carry data between various devices. The data may be carried in connection-based links, such as the virtual circuits in an asynchronous transfer mode (ATM) network. Data may also be carried between devices in network segments where data is broadcast to all of a plurality of devices on the segment via a broadcast-type medium. An example of the latter is an Ethernet network. It is typically convenient to set up local area networks (LANs) using a broadcast type medium over which devices can share data.
In some circumstances, for example, where a LAN is required to connect devices that are geographically distant from one another, the LAN may be broken into separate segments. Within each segment, devices (e.g., switches) can exchange data by way of a broadcast-type medium. The segments may be connected to one another by way of connection-based links such as physical transport lines. Such a LAN may be referred to as a virtual LAN (VLAN). The VLAN may be thought of as a logical web of connections over physical transports.
Metro-Ethernet networks are based on VLANs within the Ethernet network of a given metropolitan area. A VLAN is the interconnection, in a tree structure topology, of any number of access switches for a given customer within the larger service provider Ethernet network. The VLAN tree structure implies, that in a VLAN there can be only one path from any one access switch to another access switch. In order to provide Service Level Agreements (SLAs), a VLAN provider must be able to measure the average latency associated with traversing a VLAN. A latency measure can be calculated manually by listing all the possible paths (including the links) in a VLAN, measuring a latency value for each link and adding up the results for each path. As a VLAN becomes larger and includes more access switches and therefore more paths, it becomes increasingly complex and difficult to trace each path and to arrive at an average latency measure for the VLAN.